The long-term objectives and specific aims are directed towards the research and development of a new platelet harvesting device for separating platelet-rich plasma from 450-ml units of whole human blood from random donors for clinical use. Methodology to accomplish these goals in the "Phase I" stage of this proposed study are: (a) to scale-up the small model (21 ml) platelet separator which is based on a principle of counter-flow displacement and depth filtration; (b) to design the scaled-up system using sterile, closed and disposable bags; and (c) to evaluate systematically each of the two devices (Prototype I and II) in terms of the efficiency and quality of the collected platelet-rich plasma.